Here’s a good way to use feedback on flickr, specifically the hits counter, to critique your art. First join a Flickr group that has the largest possible audience interest in your work. I’ve joined the moleskine sketchbook group, it has 13,500 members at the time of writing. Next upload a load of art or photos to your Flickr account. Put them in a set to keep organized. Finally submit pieces from your set to the group pool.
Now you can see how many views each piece receives from the group members. From this info you can tell what’s working and what’s not. I uploaded my entire 2009 sketchbook and learned a lot about what catches peoples eye.